Determining a location of a remote radio-communication unit is useful in many applications. For example, location apparatuses and algorithms are useful for rescue operations, locating kidnapping victims, and retrieving stolen property.
Prior art location methods rely on triangularizing a signal from the radio-communication device to determine its position. One method of triangularization involves using multiple antennas whose positions are known to receive a signal transmitted by the radio-communication device. The difference between the times of receipt of the signal by the multiple antennas is used to calculate the location of the radio-communication device. A drawback to this prior-art method is that the area within which a radio-communication device can be located is limited by the coverage of the antennas. Having a sufficient amount of antennas for a system that services a large area is likely to be cost-prohibitive.
Another method of triangularizing involves the use of geolocation equipment associated with the radio-communication device. The geolocation equipment determines the coordinates of the device using geolocation satellites, and those coordinates can be transmitted by the radio-communication device to a receiver. Using geolocation has the advantage of achieving a very accurate position determination. However, geolocation equipment can be prohibitively expensive for some applications. For example, position determination can be offered as a non-essential option for a radio-communication device such as a cellular telephone. Adding the cost of geolocation equipment would drastically reduce the potential market for the cellular telephone.
Another method of determining location involves determining signal delay and Doppler effects between the radio-communication unit and a moving object. The signal delay and Doppler effects can then be used to roughly locate the radio-communication device. The advantage to this method is that position determination can be made at relatively low cost (i.e., no additional equipment is needed). However, the method leads to less accurate results due to left/right ambiguity and error inherent in the signal delay and Doppler measurements.
What are needed are a low-cost apparatus and method for accurately determining the location of a radio-communication unit.